LOL… I am sorry, but NO... Skypiea is not a heaven....
Give me a break. It has angels. Its ruled by God. Its in the clouds. Of course isn't actually heaven, but it is absolutely symbolic of heaven.
This Zoro's line actually came shows up in the very first book. I doubt that at this point of the time, Oda was planning out Skypiea… even if he did, that quote is not forshadowing the Skypiea, because in Japanese, we use the expression "My name will reach even to the heaven" meaning I will be famous enought for people in heaven know about me.
Many writers plan their stories out hugely in advance, I would be surprised if Oda didn't have at least some of the ideas for Skypedia already written down in notes or at least in his head at the begining of the series. Especially considering all of his other foreshadowing, which are a pretty big clue that hes a 'plan ahead' sort of guy.
Frankly, it doesn't matter what the actual meaning of a statement is, it can still be foreshadowing.